JPH092872A - Piezoelectric composition - Google Patents

Abstract

PURPOSE: To obtain a piezoelectric composition resistant to fracture even if large strain is developed, improved in piezoelectric properties and mechanical properties, with MgO grains smaller in size than PZT-PMN grains as the matrix phase dispersed homogeneously. CONSTITUTION: A mixture of PbO, SrCO3 , Nb2 O5 , ZrO2 and TiO2 is first calcinated and then incorporated with MgO of greater grain size followed by conducting a secondary baking to effect homogeneous dispersion of the resultant MgO grains in PZT-PMN grains as the matrix phase, thus obtaining the objective piezoelectric composition consisting of an oxide of perovskite crystal, structure having a composition of the formula Pb1-a-b Sra (Mg1/3 Nb2/3 )x Zry Tiz O3-b (in terms of atom number ratio, 0<=(a)<=0.10; 0.05<=(b)<=0.05; 0.2<=(x)<=0.5; 0.2<=(y)<=0.4; 0.3<=(z)<=0.5; (x+y+z)=1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an actuator element,
The present invention relates to a piezoelectric composition having high mechanical strength, which is suitable for a sounding element and the like.

[0002]

2. Description of the Related Art Lead zirconate titanate-based composition (PZ
T: PbZrO ₃ —PbTiO ₃ ) is known as an excellent piezoelectric element having a perovskite structure, and in addition to this PZT, a composite perovskite such as Pb (Mg _1/3 Nb _2/3 ) O _{3 is used} as a third component. In addition, a large number of piezoelectric materials have been developed that can significantly change various piezoelectric characteristics according to the composition as compared with PZT alone. These piezoelectric porcelains have high electric-mechanical energy conversion efficiency. It is used in various fields.

The element used for the actuator is preferably one that can obtain a large amount of strain or generated force at a low voltage. Further, it is preferable that the speaker and the microphone provide a large sound pressure or output voltage. Piezoelectric compositions that meet such requirements are described in JP-B-44-17103 and JP-B-4-78582.

The one described in the former is PZT.
Composition containing MN, namely Pb (Mg _1/3 N
b _2/3 ) O ₃ -PbZrO ₃ -PbTiO ₃ -based composition in which a part of Pb is replaced by Sr, Ba or Ca, and the latter is
In the above composition, the Pb composition ratio is reduced by a certain amount from the stoichiometric amount, and these are called PZT-PMN type piezoelectric bodies, and are piezoelectric porcelains having a perovskite type crystal structure as a main constituent phase. Yes, high relative permittivity and electricity −
It has a mechanical coupling coefficient and a piezoelectric strain constant.

[0005]

[Problems to be Solved by the Invention] The above-mentioned conventional PZT-
The PMN type piezoelectric body has excellent piezoelectric characteristics, but there is room for improvement in mechanical strength, and when a large signal is actually input in order to obtain a large output, the mechanical strength is insufficient, leading to destruction. There are cases.

[0006]

[Means for Solving the Problems] As a result of earnest research on means for improving mechanical properties while maintaining high piezoelectric properties, the present inventors have found that MgO, which is one of the constituent components, is added to P
It was found that high mechanical strength can be obtained by dispersing the particles between ZT-PMN particles, and further research was conducted to reach the present invention.

That is, the gist of the present invention is a piezoelectric composition having the following constitution. (1) In an oxide having a perovskite crystal structure having a composition represented by the following formula as a whole composition, PZ of a parent phase
A piezoelectric composition, characterized in that MgO particles smaller than T-PMN particles are dispersed among the particles.

Pb _1-ab Sr _a (Mg _1/3 Nb _2/3 ) x
Zr y Tiz O _3-b However, in atomic ratio, 0 ≦ a ≦ 0.10, 0.005 ≦ b
≦ 0.05 0.2 ≦ x ≦ 0.5, 0.2 ≦ y ≦ 0.4 0.3 ≦ z ≦ 0.5, x + y + z = 1.0 (2) In the piezoelectric composition of (1) above. , Ag is 0 to 0
A composition containing 0.05 mol and having an average particle size of 2 μ
A piezoelectric composition, characterized in that MgO particles having an average particle diameter of m or less are dispersed between matrix particles having an average particle diameter of 5 μm or less.

Hereinafter, the present invention will be described in detail.

Composition and Structure State The piezoelectric composition of the present invention is a PZT-PMN type piezoelectric composition having a composition similar to those described in JP-B-44-17103 and JP-B-4-78582. The basic composition range and its piezoelectric characteristics are as described in these, and do not require much explanation. That is,
In order to exhibit excellent properties as a piezoelectric body, it is necessary that the composition range be within this range, and the basic composition of the piezoelectric composition of the present invention is included in the ranges described in these. Therefore, it has a high relative permittivity and an electro-mechanical coupling coefficient, and has an excellent piezoelectric strain constant.

The difference from the conventional PZT-PMN type piezoelectric composition is that the PZT-type of the parent phase is present in the same composition range.
That is, MgO particles smaller than the PMN particles are dispersed between the PMN particles. Here, being smaller than the particles of the mother phase means that the average particle diameter of MgO is smaller than the average particle diameter of the mother phase. If the average particle size of the MgO particles is larger than the average particle size of the mother phase, cracks are likely to occur near the MgO particles, and the effect of the present invention cannot be obtained.

In the present invention, it is difficult to limit the amount of dispersed MgO particles, but as a rough guide, 100 μ
If 10 or more MgO particles are present in the square area, the effect of the present invention can be obtained. The dispersion of MgO particles can be confirmed by observation with an electron microscope. Since MgO has a smaller average atomic weight than the PZT-PMN particles of the parent phase, it can be identified because it is observed as blacker than the parent phase in the secondary electron image of a scanning electron microscope, and the dispersed state can be easily confirmed.

Manufacturing Method The manufacturing method of the piezoelectric composition of the present invention is not limited.
By having the composition and tissue state already mentioned,
Excellent piezoelectric properties and mechanical strength are obtained. A suitable manufacturing method that can obtain this composition and texture will be described below. This manufacturing method is an example and does not limit the present invention.

When mixing all the raw materials from the beginning,
An MgO raw material (MgO, MgCO _3, etc.) having a larger particle size than other raw materials is used. By using a MgO raw material having a large particle size, when the raw material is fired, a part of MgO remains unreacted, and the MgO particles are dispersed as independent particles between PZT-PMN particles generated by firing of other raw materials. Can be put into

Alternatively, a method may be used in which other raw materials except the MgO raw material are mixed and calcined, and after the calcination, the MgO raw material is mixed and secondary firing is performed. Also in this case, it is preferable that the MgO raw material has a relatively large particle size. If the particle size of MgO is too small, or if it is baked at a high temperature for a long time, the MgO particles may be absorbed by the mother phase, which is not preferable.

In any of the manufacturing methods, the piezoelectric composition of the present invention can be obtained with good reproducibility if the conditions suitable for the manufacturing process and the raw material are followed.

Control of Particle Size The piezoelectric composition of the above (2) of the present invention has the composition of the above (1)
It is the one in which 0 to 0.05 mol of g is contained by external division.
By including Ag in the above range, it becomes easy to reduce both the average particle size of the matrix and the average particle size of MgO, and there is no problem in terms of piezoelectric characteristics.

The piezoelectric composition of the present invention has enhanced mechanical strength due to the effect of dispersing MgO particles.
The piezoelectric composition of 1 allows the presence of some Ag, and
The particle size of each particle is made smaller to further increase the mechanical strength. Specifically, by adding Ag in the above content, the average particle size of the MgO particles is 2 μm or less and the average particle size of the matrix phase particles is 5 μm or less, and the mechanical strength is higher than that of particles having a larger particle size. A piezoelectric composition of is obtained.

Even if Ag is not contained, equivalent mechanical strength can be obtained as long as the average particle diameters of the matrix and MgO particles are within the above range.

[0020]

The basic composition of the piezoelectric composition of the present invention is as follows.
-17103 and Japanese Patent Publication No. 4-78582, and thus has excellent piezoelectric characteristics as described therein. The composition of (2) above contains a small amount of Ag, but this does not change the piezoelectric characteristics.

Rather, in the present invention, the mechanical strength is remarkably improved by dispersing the MgO particles between the matrix particles and controlling the particle size of these particles.

Those skilled in the art of ceramics,
It is known that particle-dispersed ceramics and ceramics having small particle diameters have high mechanical strength. These strength improving means have already been applied to ceramics for structural materials such as alumina and silicon nitride, but in ceramics such as piezoelectric ceramics that require an electrical function, there is a concern that their electrical characteristics may deteriorate, and There was little to be done.

For example, in ceramics for structural materials, alumina is often used as dispersed particles used to improve strength, but in lead-based piezoelectric ceramics, when alumina is added, Pb is absorbed by the alumina. It has been pointed out that there is a problem that the piezoelectric characteristics and the sinterability are deteriorated. Further, it has been reported that the coercive electric field increases and the relative dielectric constant decreases when the sintered particle size is reduced by alumina.

The piezoelectric composition of the present invention does not have such a problem, and it is considered that the strength can be improved without impairing the piezoelectric characteristics by using MgO, which is a part of the raw material, as dispersed particles. Within the composition range of the present invention, there is no problem in piezoelectric characteristics even if the particle size is suppressed small.

[0025]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the present invention are shown below together with comparative examples.

Example 1 Pb _0.93 Sr _0.05 (Mg _1/3 Nb _2/3 ) _0.30 Zr _0.30 T
i _0.40 O _2.98 , PbO: 206.45 g, S
rCO ₃ : 7.38 g, Nb ₂ O ₅ : 26.58 g, Z
rO ₂ : 36.97 g and TiO ₂ : 31.96 g were weighed out. Zirconia balls (diameter 3-1
(0 mm) was used as a medium for mixing for 24 hours, dried, and then calcined in an alumina box at a temperature of 800 ° C. for 2 hours. Put this calcined powder in the same mill, add 300 g of water and
Crushed for hours.

On the other hand, MgO powder having an average particle size of 4 μm was prepared and 4.03 g was weighed from this. This MgO powder was put into the mill, 40 g of a 10% PVA aqueous solution was further added, and the mixture was mixed for 2 hours. This slurry was dried by a rotary evaporator and sized through a # 100 nylon mesh to obtain a molding powder. ^T 3 using this powder
× ^w 5 × ^L 30 mm rod-shaped and ^φ 20 × ^t 2 mm disc-shaped metal mold, and further CIP at a pressure of 1.5 ton / cm ² .
(Cold isotropic pressure press).

These samples were placed in a magnesia box at 1250
Firing at 2 ° C. for 2 hours gave a sintered body. After laminating the disk-shaped sample to a thickness of 1.0 mm, bake Ag electrodes on both sides and polarize it by applying a DC voltage of 2 kV for 10 minutes in 100 ° C. silicon oil. The mechanical coupling coefficient K _r and the relative permittivity ε _r were measured (n = 10).

The rod-shaped sample was wrapped to a thickness of 2.0 mm, chamfered with # 800 emery paper, and subjected to a 3-point bending test with a span of 20 mm (n = 10).

When the structure of the fired surface of the disk sample was observed with a scanning electron microscope, the average particle size of the matrix particles was about 6 μm, and the average particle size was 2.5 μm in a 100 μm × 100 μm region. On average, 15.4 particles were dispersed. As a result of EDX (energy dispersive fluorescent X-ray) analysis of these dark particles, Mg was detected. In addition, as a result of identifying the phase of this sample by a powder X-ray diffractometer, a very weak MgO crystal phase could be detected in addition to the perovskite phase.

As a result of electrical measurement, the electromechanical coupling coefficient K _{r in} the radial direction was 65.2%, the relative dielectric constant ε _r was 4610, and the three-point bending strength was 13.4 Kg / mm ² .

That is, PZT-PMN having an average particle size of about 6 μm
A piezoelectric composition having a structure in which MgO particles having an average particle diameter of 2.5 μm are dispersed in a matrix has a K _{r of} 65.2%,
The piezoelectric property was ε _r : 4610, which was not a problem in practical use, and the three-point bending strength was 13.4 Kg / mm ² , which was a high fracture strength.

Comparative Example 1 A sintered body was obtained by the same process as in Example 1 except that MgO powder was mixed from the beginning. That is, all the raw materials containing MgO were mixed in the same composition as in Example 1, calcined under the same conditions, dried and then ground again in the same mill for 24 hours, and the same amount of binder was added and mixed for 2 hours. Perform the subsequent operations in the same way,
A sintered body was obtained.

When this sample was observed by SEM, the sintered grain size was about 6 μm, but no dark particles were found. No peak of MgO was found by XRD analysis either. Although K _r of this sample was 65.5% and ε _r was 4580, the three-point bending strength was low at 10.3 Kg / mm ² .

Comparative Example 2 A sintered body was obtained by the same process as in Example 1 except that the MgO powder used had an average particle size of 10 μm. The structure of this sample has an average particle size of 7.
2 μm of MgO particles were dispersed.

The K _r of this sample is 64.7% and ε _r is 45.
The 50-point and 3-point bending strength was 9.5 kg / mm ² , and the mechanical strength was rather low.

Example 2 In the same manner as in Example 1 except that zirconia beads having a diameter of 1.0 mm were used in place of the zirconia balls, a strong stirring type mill was used in place of the ball mill, and the residence time was 20 minutes, and calcining was performed. Then, pulverization was performed to obtain a powder. Firing temperature 11
A sintered body was obtained in the same manner as in Example 1 except that the temperature was 80 ° C.
Similarly, the structure was observed, the piezoelectric characteristics were measured, and the three-point bending strength was measured.

The structure of this sample was such that MgO particles having an average particle size of 1.5 μm were dispersed in a matrix having an average particle size of 5 μm. The K _r was 65.7% and the ε _r was 4610, showing no problem and the three-point bending strength was 15.3 kg / mm ² .

Example 3 A powder was obtained by the same steps as in Example 2 except that 3.23 g of Ag powder was added at the time of initial mixing, and the firing temperature was 1100 ° C.
A sintered body was obtained in the same manner as in Example 1 except for the above. As a result of microscopic observation, MgO particles having an average particle size of 0.8 μm were dispersed in a matrix having an average particle size of 2 μm. The SEM photographs are shown in FIGS. 1 and 2.

K _r was 65.5%, ε _r was 4640, and there were no problems, and the three-point bending strength was a high value of 16.2 kg / mm ² .

FIG. 1 is a secondary electron image obtained by an electron microscope, in which carbon is vapor-deposited on the fired surface of the sample. Further, FIG. 2 is an enlarged view of the black portion of FIG. As shown in FIG. 1, in the present sintered body, it is observed that matrix particles of about 2 μm are integrally sintered, and black portions are dispersed therebetween. It was confirmed from FIG. 2 that the black portions were constituent particles. Moreover, as a result of performing a point analysis by EDX of these black particles, a large amount of MgO was detected.

[0042]

EFFECT OF THE INVENTION The piezoelectric composition of the present invention is hard to break even when a large strain is generated, and therefore, the electrical characteristics originally possessed by this composition can be sufficiently brought out. As a result,
The industrial application range of the composition material can be greatly expanded.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the piezoelectric composition of Example 3 (magnification: 3,000 times).

FIG. 2 is an electron micrograph (magnification of 30,000) showing an enlarged black portion of FIG.

Claims (2)

[Claims] 1. An oxide having a perovskite type crystal structure having a composition represented by the following formula as a whole composition is characterized in that MgO particles smaller than PZT-PMN particles of a mother phase are dispersed among the particles. Piezoelectric composition. Pb _1-ab Sr _a (Mg _1/3 Nb _2/3 ) x Zr yTiz
O _3-b However, in atomic ratio, 0 ≦ a ≦ 0.10, 0.005 ≦ b
≦ 0.05 0.2 ≦ x ≦ 0.5, 0.2 ≦ y ≦ 0.4 0.3 ≦ z ≦ 0.5, x + y + z = 1.0 2. In an oxide having a perovskite type crystal structure having a composition represented by the following formula as a whole composition, MgO particles having an average particle size of 2 μm or less are dispersed between mother phase particles having an average particle size of 5 μm or less. A piezoelectric composition characterized in that Pb _1-ab Sr _a (Mg _1/3 Nb _2/3 ) x Zr yTiz
O _3-b + Ag _m However, in atomic ratio, 0 ≦ a ≦ 0.10, 0.005 ≦ b
≦ 0.05 0.2 ≦ x ≦ 0.5, 0.2 ≦ y ≦ 0.4 0.3 ≦ z ≦ 0.5, x + y + z = 1.00 0 ≦ m ≦ 0.05